China is set to launch the Tianwen-2 mission this year, aiming to unravel the mysteries of a "living fossil" of the solar system and one "rebel" of the main asteroid belt.

The Tianwen-2 mission aims to achieve multiple goals in a single launch: it will collect samples from the near-Earth asteroid 2016HO3, as well as explore the main-belt comet 311P.

An astronomer with the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) recently explained why these two targets are so intriguing and what cosmic secrets they might hold.

Discovered in 2016 by the Pan-STARRS telescope in Hawaii, asteroid 2016HO3, located millions to tens of millions of kilometers away from Earth, is the first quasi-satellite of Earth ever discovered. Though not a natural moon, this 40-100 meter-wide asteroid orbits the Sun with parameters almost identical to Earth's, constantly "wandering" near our planet.

"A quasi-satellite is essentially a small celestial body that orbits the Sun, just like Earth. Its trajectory is quite similar to Earth's. From our perspective on Earth, it appears to oscillate periodically around us. That's why we call it a quasi-satellite," explained Yan Wei, senior engineer at the NAOC.

Scientists believe such asteroids preserve critical information about the solar system's infancy. "These 'cosmic fossils' could reveal details about early solar system composition and evolution," Yan noted.

However, some researchers speculate the asteroid 2016HO3 might be debris from an ancient cosmic collision.

Upon arrival, the Tianwen-2 probe will photograph the asteroid's surface, analyze its rotation patterns and composition. "Comparing its material composition with that of the moon and Earth will be the focus of our exploration," Yan emphasized.

The mission also targets main-belt comet 311P, a celestial anomaly discovered in the main asteroid belt between Mars and Jupiter by American scientists in 2013. It had multiple dust tails and resembled a comet, which was highly unusual in the dry asteroid belt. Further observations confirmed that this object had the stable orbit of an asteroid but occasionally released dusts. It was thus classified as a main-belt comet and became the seventh such object ever confirmed and the most peculiar one to date.

"Main-belt comets are actually a unique type of asteroid, but exhibiting some cometary features. When they get closer to the Sun, they can release materials, including gases and particles," Yan explained.

Traditionally, comets are believed to originate from the outer edges of the solar system with large amounts of ice. When they approach the Sun, the ice evaporates, forming a spectacular tail.

Located in the main asteroid belt, a region hosting over 90 percent of the solar system's asteroids, 311P challenges astronomers' conventional understanding, as the region is too close to the Sun for the celestial body to retain its volatile materials like water ice.

Tianwen-2 will visit this "rebel" of the asteroid belt to uncover its mysteries and advance human's understanding of the solar system.